Trading Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	$ 441,414	$ 337,628	$ 211,622
Trading Securities, Net Unrealized Gain (Loss)	(986)	738	786
U.S. government agency debentures
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	20,954	6,234	18,909
Trading Securities, Net Unrealized Gain (Loss)	(9)	(4)	(8)
U.S. government agency residential mortgage-backed securities
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	365,171	310,067	122,306
Trading Securities, Net Unrealized Gain (Loss)	(1,032)	635	363
Municipal and other tax-exempt securities
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	45,444	14,427	52,721
Trading Securities, Net Unrealized Gain (Loss)	230	50	262
Other trading securities
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	9,845	6,900	17,686
Trading Securities, Net Unrealized Gain (Loss)	$ (175)	$ 57	$ 169